LHRH neurons are derived from the olfactory placode and migrate into the brain. The factors which dictate cell-specific LHRH gene expression and the migratory mechanism(s) used by the LHRH neurons during their movement in the CNS are currently unknown. Using in vivo and in vitro models, we are examining the prenatal development of the LHRH system. We are testing the hypothesis that N-CAM and fibronectin direct LHRH movement in nasal regions by using embryonic explants which maintain large numbers of LHRH expressing cells. In addition, we have found that LHRH cells do not posttranslationally modify LHRH to the amidated form in vivo until reaching the forebrain. Embryonic LHRH cells derived from nasal regions were able to produce the "mature" peptide in vitro in the absence of brain tissue, suggesting that this is a time-dependent (but not spatially-dependent) event.